A substrate such as a semiconductor wafer forming electronic elements like light emitting diodes (LED) and integrated circuits (LSI) thereon is cut into chips. A method for cutting into chips includes a laser machining method called as a stealth dicing method in which a laser beam is condensed by a field lens optical system and irradiation of the laser beam is conducted to the inside of the substrate so that a modified region having a low strength compared with the one before the irradiation is formed along a planned cutting line supposed to be set on the substrate. In this method, the substrate is cut from the modified region as an origin.
Patent document 1 discloses a method in which, when a whole region of the object for machining is separated into three portions, modified regions are formed along a planned cutting line spreading on the region in order of the near-side region, the far-side region and the central region, and displacement of the formed modified regions from the planned cutting line is inhibited.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2008-87026